Housing for a sealed electrochemical battery cell

ABSTRACT

An electrochemical cell with a collector assembly for sealing the open end of a cell container. The collector assembly includes a retainer and a contact spring with a peripheral flange, each having a central opening therein. A pressure release vent member disposed between the retainer and the peripheral flange of the contact spring seals the openings in the retainer and contact spring under normal conditions and ruptures to release pressure from within the cell when the internal pressure exceeds a predetermined limit.

BACKGROUND

The present invention relates to an electrochemical battery cell havinga housing that includes a container and a collector assembly for sealingthe electrochemical battery cell.

Batteries used as power sources for electronic equipment can store largeamounts of energy. Batteries can contain one or more electrochemicalbattery cells. Pressure inside the electrochemical battery cell canincrease due to changes in internal temperature, an increase in internalvolume of electrodes during discharge and gases generated during cellcharging, in the case of rechargeable batteries, and discharge. Suchelectrochemical battery cells typically include a mechanism forreleasing or discharging gas from the cell to limit the buildup ofinternal pressure.

Electrochemical battery cells can have an open-ended container and acollector assembly disposed at the open end of the container to closethe electrochemical battery cell. The collector assembly can include asafety pressure release vent mechanism that releases excessive pressure.

Various collector assembly and pressure release vent designs have beenused in electrochemical battery cells. For example, resealable pressurerelief vents can be found in rechargeable aqueous electrolyte cells,such as nickel-cadmium and nickel-metal hydride cells. Primary(nonrechargeable) aqueous cells, such as alkaline zinc-manganese dioxidecells, have used collector assemblies with relatively large surface areaplastic seals containing a weak section that can rupture when theinternal pressure exceeds a predetermined limit. Primary andrechargeable nonaqueous electrolyte cells, such as cells with electrodescontaining lithium metal and lithium intercalation materials, typicallyhave collector assemblies with thin-walled plastic sealing members tominimize vapor transmission and pressure relief vents that are able tovery quickly reduce internal pressure.

Examples of conventional collector assembly and pressure release ventdesigns can be found in: U.S. Pat. Nos. 4,963,446 (issued to Roels etal. Oct. 16, 1990), 5,015,542 (issued to Chaney, Jr. et al. May 14,1991), U.S. Pat. No. 5,156,930 (issued to Daio et al. Oct. 20, 1992),5,609,972 (issued to Kaschmitter et al. May 11, 1997), 5,677,076 (issuedto Sato et al. Oct. 14, 1997), 5,741,606 (issued to Mayer et al. Apr.21, 1998) and 5,766,790 (issued to Kameishi et al. Jun. 16, 1998). Eachof these examples has a large collector assembly volume or dimensionalconstraints limiting the volume within the cell for active ingredientsor a large number of components making the cell more costly anddifficult to manufacture.

SUMMARY

The present invention relates to an electrochemical battery cell havingan electrode assembly comprising positive and negative electrodes and aseparator between the electrodes, an electrolyte and a housing. Thehousing includes a container and a collector assembly. The collectorassembly has a pressure release vent member that is capable of rupturingwhen the internal pressure of the electrochemical battery cell reaches apredefined release pressure. The number and arrangement of componentswithin the collector assembly requires a small volume, thereby allowinga large volume for active materials and facilitating manufacture of aneconomical and reliable cell.

In one embodiment of the present invention, the collector assemblyincludes a retainer and a contact spring, each of which defines anopening along a pressure release channel within the electrochemicalbattery cell. The collector assembly also includes a pressure releasevent member disposed between the retainer and the contact spring and toclose the pressure release channel. When the pressure within theelectrochemical battery cell is at least as high as a predeterminedrelease pressure, the pressure release vent member ruptures allowingmatter within the cell to escape through the opening of the retainer.

In another embodiment of the invention the retainer and the contactspring peripheral flange cooperate with the pressure release vent memberto form a seal between the pressure release vent member and theretainer. The retainer can apply a compressive force to the contactspring and the pressure release vent member, via a crimp in the retainerfor example. In addition, the contact spring can further include acontinuous projection within a peripheral flange of the contact springto maintain a seal between the peripheral portion of the pressurerelease vent member and the retainer, even if the compressive forceapplied to the pressure release vent member is reduced. Furthermore, thepressure release vent member can be physically bonded to theelectrically conductive retainer by hot melting, ultrasonic welding, orby the application of an adhesive.

In yet another embodiment the collector assembly comprises a sealingmeans between the pressure release vent member and the retainer.

The pressure release vent member can include at least one layercomprising a composition that is conductive or non-conductive. Thepressure release vent member can include a composition of metal, polymeror mixtures thereof. The construction and composition of the pressurerelease vent member can be based on a vapor transmission rate ofelectrolyte that will provide a desirably low weight loss of the cell.The composition and thickness of the pressure release vent member canalso be based on the predefined or desirable release pressure at whichthe pressure release member ruptures. In one example embodiment, apressure release vent member that is a five-layer laminate ofpolyethylene teraphthalate/polyethylene/aluminum/polyethylene/lowdensity polyethylene, and which has a thickness that ranges from about0.0254 mm (0.001 inch) to about 0.254 mm (0.010 inch) has a releasepressure that ranges from about 14.1 kg/cm² (200 lbs/in²) to about 42.3kg/cm² (600 lbs/in²) at room temperature (20° C. to 25° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale.Also, in the drawings, like reference numerals designate correspondingparts throughout the several views.

FIG. 1 is a cross-sectional view of an electrochemical battery cellaccording to an embodiment of the invention;

FIG. 2 is a cross-sectional view of the top portion of anelectrochemical battery cell and collector assembly of the prior art;

FIG. 3 is a cross-sectional view of the top portion of anelectrochemical battery cell and collector assembly according to anembodiment of the invention;

FIG. 4 is a cross-sectional view of the top portion of anelectrochemical battery cell and collector assembly according to anembodiment of the invention; and

FIG. 5 is a cross-sectional view of a test membrane used in a VaporTransmission Rate test.

DETAILED DESCRIPTION

FIG. 1 shows a cylindrical electrochemical battery cell 100 according toan embodiment of the present invention. Electrochemical battery cell 100of the present invention has a housing 102 that includes a container 104and a collector assembly 106. The container 104 has a closed bottom andan open top end that is closed by the collector assembly 106. Thecontainer 104 also has a bead 107 that separates the top and bottomportions of the container 104. Disposed within the bottom portion of thecontainer 104 is an electrode assembly 108 that includes a negativeelectrode or anode 110, a positive electrode or cathode 112, and aseparator 114 disposed between the anode 110 and the cathode 112. In theexample embodiment shown in FIG. 1, the anode 110, cathode 112 andseparator 114 are each thin sheets which are wound together in a spiral,also known as a “jelly roll” design. Electrochemical battery cell 100 iscylindrical, however, one skilled in the art can appreciate thatalternative embodiments of the present invention can also include cellsand electrodes of other shapes. The container 104 can be one of severalgeometric shapes, for example, prismatic and rectangular.

If electrochemical battery cell is a lithium electrochemical batterycell, the anode 110 contains lithium metal, which can be in the form ofa sheet or foil. A cathode 112 for a lithium cell can contain one ormore active materials, usually in particulate form. Any suitable activecathode material may be used, and can include, for example, FeS₂, MnO₂,CF_(x), and (CF)_(n). Suitable separator materials are electricallynon-conductive but are ion-permeable to electrolyte. Electrolytes thatare used in a lithium electrochemical battery cell typically compriseorganic solvents. Further detail regarding the material compositionsused for the anode 110, cathode 112, separator 114 and electrolyte oflithium as well as various other electrochemical battery cells aredescribed below.

The container 104 can be a metal can with an integral closed bottom,however, a metal tube that is initially open at both ends may also beused. The cell container 104 can be a steel that is optionally plated,for example, with nickel, on at least the outside to protect the outsideof the container 104 from corrosion or to provide a desired appearance.Also, the type of steel can depend in part on the manner in which thecontainer 104 is formed. For example, containers which are made using adrawing process can be made of a diffusion annealed, low carbon,aluminum killed, SAE 1006 or equivalent steel, with a grain size of ASTM9 to 11 and equiaxed to slightly elongated grain shape. Other metals maybe used to meet particular needs. For example, for an electrochemicalbattery cell 100 in which the container 104 is in electrical contactwith the cathode 112, the open circuit voltage of the cell is about 3volts or more, or the cell is rechargeable, a more corrosion-resistantcontainer material than steel may be desired. Such materials include butare not limited to stainless steels, nickel plated stainless steels,nickel clad stainless steels, aluminum and alloys thereof.

The collector assembly 106 which is disposed in the top portion of thehousing 102 can include a positive contact terminal 116, a retainer 118which defines an opening, a pressure release vent member 120, a contactspring 122 which defines an opening, and a gasket 124 which ispositioned between these components and the container 104. The collectorassembly 106 can optionally include a positive temperature coefficient(PTC) device 126, which defines an opening, disposed between theretainer 118 and the positive contact terminal 116. The positive contactterminal 116 which protrudes above the container 104 is held in place bythe inwardly crimped top edge 128 of the container 104 and the gasket124.

The cathode 112 of the electrode assembly 108 is electrically connectedto the collector assembly 106 by contact spring 122. The contact spring122 can have at least one tab 134 that is biased against the upper edgeof the current collector 136 which is disposed at the top of theelectrode assembly 108. The current collector 136 is an electricallyconductive substrate, for example a metal substrate, on which thecathode materials are disposed, that extends beyond the cathodematerials and the separator 114. The current collector 136 may be madefrom copper, copper alloy, aluminum, aluminum alloy, and other metals aslong as they are stable inside the cell. The current collector 136 canbe in the form of a thin sheet, a foil, a screen or expanded metal. Thecontact spring 122 can be made of one or more conductive materialshaving spring-like characteristics, including for example, shape memoryalloys. When the collector assembly 106 is placed into container 104during assembly, the current collector 136 can push against the tab 134of the contact spring 122, which has a composition that is resilient toforce. This helps ensure contact between the tab 134 and the currentcollector 136. The contact spring 122 can have more than one tab 134 forcontacting the current collector 136. In some embodiments electricalcontact between the tab 134 and the current collector is maintained bythe spring-like force applied by the tab 134 against the currentcollector 136. In other embodiments the tab 134 can be welded to thecurrent collector 136. In yet other embodiments the tab 134 is connectedto the current collector 136 with an electrically conductive lead, suchas a narrow metal strip or wire welded to both the tab 134 and thecurrent collector 136. Welded connections can sometimes be morereliable, especially under extreme handling, storage and use conditions,but pressure connections do not require additional assembly operationsand equipment.

The anode 110 is electrically connected to the inner surface of thecontainer 104 by a metal anode lead (not shown), and the electrodeassembly 108 is otherwise physically separated from the container 104 byan outer wrap of the separator 114 and an insulator 138 which is locatedaround the peripheral portion of the top of the electrode assembly 108to prevent the current collector 136 from making contact with thecontainer 104. Contact between the bottom edge of the cathode 112 andthe bottom of the container 104 is prevented by the inward-foldedextension of the separator 114 and an electrically insulating bottomdisc (not shown) positioned in the bottom of the container 104.

During normal operation of the electrochemical battery cell 100, anelectrical device (not shown) can make contact with the positive contactterminal 116 of the collector assembly 106 at one end, and the negativecontact terminal at the closed end of container 104. A conductive pathis thus established between the negative terminal or container 104,through the anode lead, through the electrode assembly 108, through thecurrent collector 136, and to the collector assembly 106. The currentpath through the collector assembly 106 is through the tab 134 of thecontact spring 122, across the retainer 118, around the pressure releasevent member 120, and to the positive contact terminal 116. The retainer118 can be made of one or more conductive materials, such as metal,bimetal, and tri-layer laminated materials. For example, the retainer118 can be a metal such as nickel plated steel or stainless steel or aclad metal of combinations of steel, stainless steel, copper, aluminum,nickel and alloys thereof.

The positive contact terminal 116 should have good resistance tocorrosion by water in the ambient environment as well as good electricalconductivity. Positive contact terminal 116 can be made from aconductive material, such as a nickel plated cold rolled steel or asteel that is nickel plated after the contact terminals are formed. Thematerial used can also depend upon the complexity of the shape of thepositive contact terminal 116. If the positive contact terminal 116 hasa complex shape, then for example, a type 304 soft annealed stainlesssteel with ASTM 8 to 9 grain size may be used to provide the desiredcorrosion resistance in ease of metal forming. Once formed, the positivecontact terminal 116 may also be plated with various metals, such asnickel.

The gasket 124 provides a seal for the collector assembly 106 againstthe top portion of container 104. The gasket 124 can extend from theinsulator 138, which physically separates the current collector 136 fromthe lower portion of container 104 below the bead 107, to the edge 128of the top portion of container 104. The contour of the top portion ofthe container 104 includes the bead 107 which provides a seating surface140 for the collector assembly 106. Gasket 124 physically separates theconductive components of the collector assembly 106 from the top portionof the container 104 and also seals the peripheral edges of thecomponents of the collector assembly 106 to prevent corrosion andleakage of electrolyte between these components. The gasket 124 is sizedso that upon inserting of the collector assembly 106 into the container104 and crimping the top edge 128 of the container 104 and gasket 124,the gasket 124 is compressed to create a seal between the gasket 124 andthe container 104 as well as between the gasket 124 and interfacialsurfaces of the other components of the collector assembly 106.

The gasket 124 can be made of a material composition that can form acompression seal and that also has a low vapor transmission rate (VTR)in order to minimize the entry of water into the cell and the loss ofelectrolyte from the electrochemical battery cell 100. Gasket 124 can bemade of a polymeric composition, for example, a thermoplastic orthermoset polymer, the composition of which is based in part on thechemical compatibility of the anode 110, cathode 112 and electrolyteused in the electrochemical battery cell 100. Examples of materials thatcan be used in a gasket 124 for a non-aqueous cell, such as a lithium orlithium ion cell, include but are not limited to, polypropylene,polyphenylene sulfide, tetrafluoride-perfluoroalkyl vinyl etherco-polymer, polybutylene terephthalate (PBT), ethylenetetrafluoroethylene, polyphthalamide, and blends thereof. A suitableprolypropylene that can be used is PRO-FAX® 6524 from BasellPolyolephins, of Wilmington, Del., USA. A suitable polyphenylene sulfideis available as TECHTRON® PPS from Boedeker Plastics, Inc. of Shiner,Tex., USA. The polymers can also contain reinforcing inorganic fillersand organic compounds in addition to the base resin.

A pressure release channel 142 of electrochemical battery cell 100 isdefined by the opening of the retainer 118 and the opening of thecontact spring 122. The closing of the electrochemical battery cell 100and the pressure release channel 142 is completed by the pressurerelease vent member 120 disposed across the openings in the retainer 118and the contact spring 122. A seal is formed between the peripheralportion of the pressure release vent member 120 and at least one of theretainer 118 and the contact spring 122. This seal can be a result oftight pressure contact at the interfacial surface(s), which can, in someembodiments, be enhanced by compression of the peripheral portion of thepressure release vent member 120. Optionally, an adhesive or sealant canbe applied to the interfacial surface(s), as described below. Theperipheral portion of at least one of the retainer 118 or the contactspring 122 can also serve to bias the peripheral portion of the pressurerelease vent member 120 against the sealing interfacial surface(s) as aresult of axial forces placed on the gasket 124 and peripheral portionsof the other components of the collector assembly 106 when the top edgeof the container 104 and gasket 124 are crimped. The pressure releasevent member biasing characteristics of the retainer 118 and the contactspring 122 can be achieved by using suitable materials and suitablegeometric shapes along the peripheral flange of the contact spring 122and the retainer 118 therefor.

During normal operation of electrochemical battery cell 100, gases aregenerated within the cell through chemical reactions. As the internalpressure builds within the electrochemical battery cell 100, thecontents are substantially contained within the electrochemical batterycell 100 by the pressure release vent member 120. As the internalpressure builds the pressure release vent member 120 may deform;however, axial compressive force exerted by the container 104 on thecollector assembly 106, as described above, can cause the pressurerelease vent member 120 remain substantially in place to prevent escapeof the gases and cell contents through the opening of retainer 118. Thecompression of the collector assembly 106 within the electrochemicalbattery cell 100 can at least prevent the pressure release vent member120 from creeping inwardly so far as to form an opening in the pressurerelease channel 142 between the opening of retainer 118 and the openingof contact spring 122 when the cell pressure is less than thepredetermined release pressure.

However, when the pressure within the electrochemical battery cell 100is at least as high as a predetermined release pressure, the pressurerelease vent member 120 ruptures and allows matter, in the form of gasor liquid or both, within the cell to escape through the opening of theretainer 118. The matter within the cell can escape through the one ormore vent holes 130 in the positive contact terminal 116. Thepredetermined release pressure can vary according to the chemical typeand the integrity of the electrochemical battery cell 100 in view ofsafety and environmental requirements. For example, in an AA size or AAAsize lithium battery, the predetermined release pressure, i.e. thepressure at which the pressure release vent member 120 creates anopening, for example, via rupturing, can range from about 10.5 kg/cm²(150 lbs/in²) to about 42.3 kg/cm² (600 lbs/in²) and in someembodiments, from about 14.1 kg/cm² (200 lbs/in²) to about 28.1 kg/cm²(400 lbs/in²) at room temperature. The pressure at which the pressurerelease vent member ruptures can be determined by pressurizing a cell,e.g., through a hole punctured in the container.

As mentioned above, the electrochemical battery cell 100 can optionallyinclude a PTC device 126 which defines an opening and is disposedbetween the retainer 118 and the positive contact terminal 116. Duringnormal operation of the electrochemical battery cell 100, current flowsthrough the PTC device 126. If the temperature of the electrochemicalbattery cell 100 reaches an abnormally high level, the electricalresistance of the PTC device 126 increases to reduces the current flow.The PTC device 126 can slow or prevent cell continued internal heatingand pressure buildup resulting from electrical abuses such as externalshort circuiting, abnormal charging and forced deep discharging.However, if internal pressure continues to build to the predeterminedrelease pressure, the pressure release vent member 120 ruptures torelieve the internal pressure.

The pressure release vent member 120 disposed between the retainer 118and the contact spring 122, includes at least one layer of a compositionof metal, polymer, or mixtures thereof. It is also possible that thepressure release vent member 120 can include two or more layers ofdifferent material compositions. For example, a second layer having adifferent composition than a first layer may be used for purposes ofbonding the pressure release vent member 120 to the retainer 118 or tothe contact spring 122. In another example, a second and a third layerhaving a different composition than the first layer, may be used to bondthe pressure release vent member 120 to both the retainer 118 and thecontact spring 122. Also, multiple layers having two or morecompositions can be used for tailoring the performance properties, forexample, strength and flexibility, of the pressure release vent member120.

Compositions suitable for use in the pressure release vent member 120can include, but are not limited to, metals such as aluminum, copper,nickel, stainless steel, and alloys thereof; and polymeric materialssuch as polyethylene, polypropylene, polybutylene terephthalate (PBT),polyethylene terephthalate (PET), ethylene acrylic acid, ethylenemethacrylic acid, polyethylene methacrylic acid, and mixtures thereof.The composition of the pressure release vent member 120 can also includepolymers reinforced with metal, as well as a single layer or amulti-layer laminate of metals or polymers or both. For example, thesingle layer can be a metal that is substantially impermeable to water,carbon dioxide and electrolyte, or a non-metallized film of a polymercoated with a layer of oxidized material that prevents vaportransmission, such as, for example, SiO_(x) or Al₂O_(x). The pressurerelease vent member 120 can furthermore contain an adhesive layer thatcontains, for example, polyurethane, and a heat sealable layer thatcontains, for example, low density polyolefins.

Alternatively, an adhesive or other type of sealant material can beapplied to a portion of the pressure release vent member, the retaineror both for enhancing the seal within the collector assembly.

Regardless of the composition, the pressure release vent member 120should be chemically resistant to the electrolyte contained in the cell100 and should have a low vapor transmission rate (VTR) to provide a lowrate of weight loss for the cell 100 over a broad range of ambienttemperatures. For example, if the pressure release vent member 120 ismetal which is impervious to vapor transmission, the VTR through thethickness of the pressure release member 120 is substantially zero.However, the pressure release vent member 120 can include at least onelayer of vapor-permeable material, for example polymeric materials, asdescribed above, that can function, for example, as an adhesive or as anelastomeric layer to achieve a seal between the pressure release ventmember 120 and at least one of the retainer 118 and the contact spring122.

The VTR measured at 75° C. of a layer of the pressure release ventmember 120 according to example embodiments of the present invention canbe less than about 11.81 g·mm/(day·mm²) {3000 g·mil/(day·in²)}, and insome embodiments can range from about 0.1969 g·mm/(day·mm²) {50g·mil/(day·in²)} to about 11.81 g·mm/(day·mm²) {3000 g·mil/(day·in²)},in alternative embodiments, from about 0.3543 g·mm/(day·mm²) {90g·mil/(day·in²)} to about 9.84 g·mm/(day·mm²) {2500 g·mil/(day·in²)},and in yet alternative embodiments, from about 0.3543 g·mm/(day·mm²) {90g·mil/(day·in²)} to about 5.9 g·mm/(day·mm²) {1500 g·mil/(day·in²)}. TheVTR can vary according to the composition of the electrolyte containedin the electrochemical battery cell 100, in addition to the compositionof a vapor-permeable layer of the pressure release vent member 120 whichcan be chosen such that the VTR is within the desired limits. Pressurerelease vent members having more than one layer of material and the testprocedure for calculating the VTR are described in more detail below.

The predetermined release pressure, or the pressure at which thepressure release vent member 120 is intended to rupture, is a functionof its physical properties (e.g., strength), its physical dimensions(e.g., thickness) and the area of the opening defined by the retainer118 and the opening defined by the PTC device 126, whichever is smaller.The greater the exposed area of the pressure release vent member 120 bythe retainer 118 and the PTC device 126, the lower will be thepredetermined release pressure due to the greater collective forceexerted by the internal gases of the electrochemical battery cell 100.

The thickness of the pressure release vent member 120 can be less thanabout 0.254 mm (0.010 inch), and in some embodiments can range fromabout 0.0254 mm (0.001 inch) to about 0.127 mm (0.005 inch), and in yetother embodiments the thickness can range from about 0.0254 mm (0.001inch) to about 0.05 mm (0.002 inch). The composition and thickness ofthe pressure release vent member 120 can be determined by those ofordinary skill in the art, in view of the vapor transmission rate (VTR)and predetermined release pressure requirements.

FIG. 2 shows a cross-sectional view of the top portion of anelectrochemical battery cell 200 of the prior art. The electrochemicalbattery cell 200 includes a housing 202 that includes a container 204having a bead 207 that separates the top and bottom portions of thecontainer 204, and an open end that is closed by collector assembly 206.Collector assembly 206 includes a positive contact terminal 216 havingone or more vent holes 230, a gasket 224, a PTC device 226, a cell cover244, a bushing 246, a vent ball 248, and a contact spring 222 that is inphysical contact with the current collector 236 which extends from theelectrode assembly (not shown) in the bottom portion of container 204.The current collector 236 is otherwise physically separated from thecontainer 204 by an insulator 238. The cell cover 244 has a vent well250 that projects downward away from the positive contact terminal 216internal to the electrochemical battery cell 200. The vent well 250 hasa vent aperture 252 formed therein which is sealed by the vent ball 248and vent bushing 246 when they are seated in the vent well 250 such thatthe bushing 246 is compressed between the vent ball 248 and the verticalwall of the vent well 250. When the internal pressure of theelectrochemical battery cell 200 exceeds a predetermined level, the ventball 248, and in some cases both the bushing 246 and the vent ball 248,are forced away from the vent aperture 252 and at least partly out ofthe vent well 250 to release pressurized gas through the vent aperture252 and vent holes 230 of electrochemical battery cell 200.

With reference to the example embodiment of the present invention shownin FIG. 1, the vertical height, h1, of the top portion, or shoulder, ofcontainer 104 of electrochemical battery cell 100, is less than thevertical height, h2, of the top portion of container 204 ofelectrochemical battery cell 200 in FIG. 2. The shoulder height, h1(FIG. 1), measured outside the container 104 from the top of container104 to the seating surface 140 of bead 107, is less than the shoulderheight, h2 (FIG. 2), measured outside container 204, from the top ofcontainer 204 to the seating surface 240 of bead 207. The collectorassembly 106 shown in FIG. 1 consumes less vertical height, or shoulderheight, than the collector assembly 206 of the prior art of FIG. 2,thereby allowing for greater volume in the bottom portion of thecontainer 104 in electrochemical battery cell 100 to accommodate activeelectrode materials. The pressure release vent member 120 (FIG. 1),being substantially flat, consumes less vertical space than the cellcover 244 having vent well 250 (FIG. 2). As a result, the top portion ofa conventional AA size lithium/FeS₂ electrochemical battery cell 200 hasa shoulder height h2 of about 3.175 mm (0.125 inch), whereas the topportion of AA size lithium/FeS₂ electrochemical 100 in an exampleembodiment of the present invention can have a shoulder height h1 ofabout 2.667 mm (0.105 inch) or less. In addition, the collector assembly106 (FIG. 1) has fewer parts than the collector assembly 206 (FIG. 2) ofthe prior art, which allows for greater ease and flexibility in assemblyand manufacturing, thereby reducing costs.

FIG. 3 is a cross-sectional view of the top portion of anelectrochemical battery cell 300 and the collector assembly 306according to another example embodiment of the invention. Theelectrochemical battery cell 300 includes a housing 302 that includes acontainer 304 having a bead 307 between the top and bottom portions ofthe container 304, and an open end that is closed by collector assembly306. Collector assembly 306 includes a positive contact terminal 316having one or more vent holes 330, a gasket 324, a retainer 318 thatdefines an opening, a pressure release vent member 320, and a contactspring 322 which defines an opening and which has a tab 334 that is inphysical contact with the current collector 336 which extends from theelectrode assembly (not shown) in the bottom portion of container 304.The opening of retainer 318 and opening of contact spring 322 define anopening along pressure release channel 342, and the pressure releasevent member 320 is disposed across the openings of retainer 318 andcontact spring 322 to close the pressure release channel 342 betweenretainer 318 and contact spring 322. Optionally, the collector assembly306 can include a PTC device 326 that defines an opening, disposedbetween the retainer 318 and the positive contact terminal 316.

The collector assembly 306 is similar to the collector assembly 106 ofFIG. 1, however, the retainer 318 has a crimp 319, for example aC-shaped crimp, which directly contacts both the contact spring 322 andthe pressure release vent member 320 and provides an axial force to holdthe periphery of the pressure release vent member 320 against theretainer 318 and the contact spring 322. The crimp 319 of retainer 318has high strength in both the radial and axial directions and canwithstand high radial and axial compressive sealing force to retain thepressure release vent member 320 substantially in place when theinternal pressure builds inside the electrochemical battery cell 300.When the pressure builds the pressure release vent member 320 may deformor bulge, but the compressive force can maintain a seal between theretainer 318 and the pressure release vent member 320 when the internalcell pressure is less than the predetermined release pressure.

In addition, contact spring 322 can include a peripheral flange that hasa projection 332 that can improve the seal between the peripheralportion of the pressure release vent member 320 and the retainer 318.The peripheral flange of the contact spring 322 can be a continuousannular flange and the projection 332 can be a continuous projectioncompletely surrounding the central opening in the spring 322.Alternatively, the projection 322 can be discontinuous, comprising aplurality of separate projections. The projection 332 has a shape thathelps maintain a compressive force against the peripheral portion of thepressure release vent member 320 when the crimp 319 of the retainer 318undergoes springback and stress relaxation and moves away from thecontact spring 322. The projection 332 shown in the example embodimentof FIG. 3 is a downward and inward rolled edge of the peripheral flangeof the contact spring 322; however, projections that project upward andthat have alternative profiles are possible.

Contact spring 322 can also have an extending wall 323 that may exert aradial compressive force against the gasket 324. This can improve theeffectiveness of sealing the open end of the container 304 by providingan additional internal seal between the contact spring 322 and thegasket 324. This can increase the length of the interfacial sealingsurface between the gasket 324 and collector assembly 306 and keepelectrolyte from the peripheral portion of the pressure release ventmember 320. It can also shield the peripheral edge of the contact spring322 and the bottom edge of the retainer 318 from electrolyte to preventcorrosion.

Alternatively, the retainer can be in the shape of a washer, as in cell100 in FIG. 1, and the peripheral flange of the contact spring caninclude a portion that is crimped up and over a peripheral portion ofthe retainer.

FIG. 4 illustrates electrochemical battery cell 400 according to analternative embodiment of the present invention. Electrochemical batterycell 400 includes a housing 402 that includes a container 404 having abead 407 that separates the top and bottom portions of the container404, and an open end that is closed by collector assembly 406. Collectorassembly 406 includes a positive contact terminal 416 having one or morevent holes 430, a gasket 424, a retainer 418 having an opening, apressure release vent member 420, and a contact spring 422 having a tab434 that is in physical contact with the current collector 436 whichextends from the electrode assembly (not shown) in the bottom portion ofcontainer 404. Optionally, the collector assembly 406 can include a PTCdevice 426 disposed between the retainer 418 and the positive contactterminal 416.

As in the retainer 318 of electrochemical battery cell 300 (FIG. 3), theretainer 418 of electrochemical battery cell 400 (FIG. 4) has a crimp419, for example a C-shaped crimp, that contacts the pressure releasevent member 420 and contact spring 422. The retainer 418, the contactspring 422, and the pressure release vent member 420 cooperate to forman electrolyte seal within the collector assembly 406. Contact spring422 has a peripheral flange with a projection 432 in the form of adownward projecting annular groove with a V-shaped profile, althoughalternative geometries and profiles of the projection 432 are possible.The peripheral flange of contact spring 422 can be a continuous (e.g.,annular) flange, and the projection 432 can be continuous (e.g., anannular projection) along the peripheral flange of contact spring 422.

As described above, the predefined release pressure of theelectrochemical battery cell 400, which is the pressure at which thepressure release vent member 420 ruptures, can be controlled by varyingthe size of the opening of retainer 418. For a given material type andthickness, the release pressure of the electrochemical battery cell canbe decreased by increasing the opening defined by retainer 418, assumingthe pressure release vent member 420 has the same thickness andcomposition, because more outward force will be exerted on the pressurerelease vent member 420. For example, the opening defined by retainer418 is smaller than the opening defined by retainer 318 (FIG. 3), andtherefore, the predefined release pressure of electrochemical batterycell 400 is greater than the predefined release pressure ofelectrochemical battery cell 300 (FIG. 3). The above also assumes thatthe opening of the PTC device 426 is at least as large as the openingdefined by the retainer 418.

In an alternative embodiment, the electrochemical battery cell 400 (FIG.4) can have a collector assembly 406 that can include an optionalinternal gasket in addition to gasket 424. The internal gasket isdisposed between the pressure release vent member 420 and at least oneof the retainer 418 and contact spring 422 to provide an electrolyteseal. The internal gasket can improve the effectiveness of sealing thepressure release vent member 420 against the surrounding metalcomponents when the collector assembly 406 is placed into the container404. The internal gasket can be made of one of several materials, forexample elastomeric materials, described above with regards to gasket124 (FIG. 1), and it can be an adhesive-coated material to provide anadhesive bonded seal. The internal gasket can have a C-shaped profiledisposed between the retainer 418 and both the contact spring 422 andthe pressure release vent member 420, but the internal gasket can have avariety of shapes. For example, the internal gasket can be asubstantially flat washer disposed between the retainer 418 and theupper surface of the peripheral portion of the pressure release ventmember 420, between the pressure release vent member 420 and the uppersurface of the peripheral portion of the contact spring 422, or in bothof these locations. The internal gasket can also be L-shaped, orientedin an upright or inverted position, such that a vertical wall of theinternal gasket is disposed around the outer edges of the peripheralportions of the pressure release vent member 420 and the contact spring422, as long as there is an electrical contact between the contactspring 422 and the retainer 418. Such an L-shaped configuration, as wellas the C-shaped geometry, can seal electrolyte from the peripheralportion of the pressure release vent member 420. Similar internalgaskets can be included in alternative embodiments of electrochemicalbattery cells 100, 300, illustrated in FIGS. 1 and 3, respectively, aswell as in other embodiments.

In cell 400 the pressure release vent member 420 includes a first layer420 a, a second layer 420 b and a third layer 420 c. For example, thesecond layer 420 b, which is disposed between the first layer 420 a andthe retainer 418, and the third layer 420 c, which is disposed betweenthe first layer 420 a and the contact spring 422, can function as anadhesive or a sealable layer to seal the pressure release vent member420 against the retainer 418 and contact spring 422. As in any of theexample embodiments the pressure release vent member 420 can be bondedto the retainer 418 or the contact spring 422, or both, by one severalmethods, for example, adhesive bonding, spot welding, ultrasonic weldingor other welding and attachment methods known by those skilled in theart. It is also possible that the pressure release vent member 420 canbe held in place mechanically such that layers of adhesives and heatsealable materials are not needed. The second layer 420 b and the thirdlayer 420 c can also function as a protective coating to prevent marringor rupture of the first layer 420 a during assembly.

As described above with respect to electrochemical battery cell 100(FIG. 1), the pressure release vent member 120 (FIGS. 1, 3) and 420(FIG. 4) can include at least one layer of a composition containingmetal, polymer, and mixtures thereof. A suitable three-layer laminatethat can be used for the pressure release vent member 420 isPET/aluminum/EAA copolymer available as LIQUIFLEX® Grade 05396 35C-501Cfrom Curwood of Oshkosh, Wis., USA. A suitable five-layer laminate isPET/PE/Aluminum/PE/LLDPE available as BF-48 from Ludlow Coated Productsof Columbus, Ga., USA, which is a wholly-owned subsidiary TycoInternational, Ltd. of Princeton, N.J., USA.

The VTR ranges of any permeable layer of the pressure release ventmember 120 (FIG. 1), 320 (FIG. 3), and 420 (FIG. 4) as described abovecan be determined using a method adapted from ASTM E96-80 (Standard TestMethod for Water Vapor Transmission of Materials). A test membrane 501(FIG. 5) having a composition of a permeable layer of the pressurerelease vent member, for example pressure release vent members 120, 320,420, is placed over the top of a 15 ml bottle (e.g., Wheaton SerumBottle, 25 mm diameter×54 mm high, Cat. No. 06-406D) that is 25 mmdiameter by 54 mm high and contains 8 ml of the electrolyte to be usedin a cell. The vent membrane 501 has a wall 503, a hub 505 and a testsurface 507 sized to provide a seal against the bottle. The outerdiameter of wall 503 is 19.56 mm and the inner diameter of wall 503 is14.33. The hub 505 has a diameter of 3.23 mm and a length below the testsurface 507 of 1.91 mm. The test surface 507 has a thickness of 0.508 mmand a test surface area, which is the annular area between wall 503 andhub 505, of 1.529 cm². Vacuum grease is applied to the lip of thebottle, and a seal (e.g., Wheaton Aluminum Seal Cat. No. 060405-15)having a 15.88 mm diameter center hole is placed over the test membraneand crimped tightly onto the bottle such that the test membrane 501 willremain sealed to the bottle during the test. The sealed bottle isweighed and the bottle is stored at 75° C. and weighed at regularintervals within a predetermined test period (e.g. monthly for sixmonths, daily for two weeks, etc.). The change in weight is determinedover the test period and the first experimental VTR is calculated. Thesame test is performed on a sealed empty bottle as described above andthe change in weight is determined over the same regular intervals andtest period, and the second experimental VTR is calculated. Each of thefirst and second experimental VTR is calculated using the average totalweight loss. Finally, the second experimental VTR calculated for thetest run on the empty bottle is subtracted from the first experimentalVTR calculated for the test run on the bottle containing electrolyte toobtain the VTR of the test membrane.

Materials that can be used for the electrode assembly and theelectrolyte in the embodiments of the present invention, including butnot limited to the example embodiments described above in FIGS. 1, 3,and 4, are described as follows. The anode in a lithium electrochemicalbattery cell contains lithium metal, often in the form of a sheet orfoil. The composition of the lithium can vary, though the purity isalways high. The lithium could be alloyed with other metals such asaluminum, to provide the desired cell electrical performance. The anodefor a lithium ion cell includes one or more lithium-intercalablematerials. By intercalable materials it is meant that the material iscapable of insertion and de-insertion of lithium ions into theircrystalline structure. Examples of suitable materials include, but arenot limited to, carbons such as graphitic, mesophase and/or amorphiccarbons; transition metal oxides such as nickel, cobalt and manganese;transition metal sulfides, for example, those of iron, molybdenum,copper and titanium; and amorphous metal oxide, for example thosecontaining silicone and tin. These materials are generally particulatematerials that are formed into the desired shape.

A cathode for a lithium cell contains one or more active materials,usually in particulate form. Any suitable active cathode material may beused, and can include for example FeS₂, MnO₂, CF_(x) and (CF)_(n). Acathode for a lithium ion cell contains one or more lithium-intercalatedor lithium-intercalable materials, usually in particulate form. Examplesinclude metal oxides, such as vanadium and tungsten; lithiatedtransition metal oxides, for example, nickel, cobalt and manganese;lithiated metal sulfides for example those of iron, molybdenum, copperand titanium; and lithiated carbons.

Suitable separator materials are ion-permeable and electricallynon-conductive. Examples of suitable separators include microporousmembranes made from materials such as polypropylene, polyethylene andultra high molecular weight polyethylene. A suitable separator materialfor Li/FeS₂ cells is available as CELGARD®2400 microporous polypropylenemembrane from Celgard Inc., of Charlotte, N.C., USA, and Setella F20DHImicroporous polyethylene membrane available from Exxon Mobil ChemicalCompany of Macedonia, N.Y., USA. A layer of a solid electrolyte or apolymer electrolyte can also be used as a separator.

Electrolytes for lithium and lithium ion cells are non-aqueouselectrolytes and contain water only in very small quantities, forexample, less than about 500 parts per million by weight, as acontaminant. Suitable non-aqueous electrolytes contain one or moreelectrolyte salts dissolved in an organic solvent. Any suitable salt maybe used depending on the anode and cathode active materials and thedesired cell performance. Examples include lithium bromide, lithiumperchlorate, lithium hexafluorophosphate, potassium hexafluorophosphate,lithium hexafluoroarsonate, lithium trifluoromethanesulfonate andlithium iodide. Suitable organic solvents include one or more of thefollowing: dimethyl carbonate; diethyl carbonate; dipropyl carbonate;methylethyl carbonate; ethylene carbonate; propylene carbonate;1,2-butylene carbonate; 2,3-butylene carbonate; methaformate;gamma-butyrolactone; sulfolane; acetonitrile; 3,5-dimethylisoxazole;n,n-dimethylformamide; and ethers. The salt and solvent combinationshould provide sufficient electrolytic and electrical conductivity tomeet the cell discharge requirements over the desired temperature range.When ethers are used in the solvent they provide generally lowviscosity, good wetting capability, good low temperature dischargeperformance and high rate discharge performance. Suitable ethersinclude, but are not limited to, acyclic ethers such as1,2-dimethoxyethane (DME); 1,2-diethoxyethane; di(methoxyethyl)ether;triglyme, tetraglyme and diethylether; cyclic ethers such as1,3-dioxolane (DIOX), tetrahydrofliran, 2-methyl tetrahydrofuran and3-methyl-2-oxazolidinone; and mixtures thereof.

Electrochemical battery cells according to the invention can be of atype other than lithium and lithium ion cells. Examples include bothprimary and rechargeable cells with aqueous electrolytes, such aszinc/MnO₂, zinc/NiOOH, nickel/cadmium and nickel/metal hydride alkalinecells. These types of cells can have alkaline electrolytes with solutessuch as potassium hydroxide, sodium hydroxide and mixtures thereof.

The electrochemical battery cells 100, 300 and 400 can be assembled byany suitable process. For example, the electrochemical battery cell 100of FIG. 1 can be made by inserting the electrode assembly 108 and theinsulator 138 into the cell container 104 and then dispensingelectrolyte into the container 104. The gasket 124, the contact spring122, the retainer 118, the pressure release vent member 120, and,optionally, the PTC device 126 are then placed in the open end of thecontainer 104. The container 104 is supported at the bead 107 while thecollector assembly 106 including gasket 124 and positive contactterminal 116 are pushed downward against the seating portion 140 of thebead 107 and the top edge of the container 104 is bent inward so thatthe container 104 is compressed against gasket 124 to complete thesealing of the open end of the housing. Any suitable method may be usedto seal the electrochemical battery cell 100, such as deforming thecontainer 104 by crimping, colleting, swaging, or redrawing.

In an alternative embodiment, the pressure release vent 120 can bebonded to the retainer 118 by one or more several methods, such as byhot melting, ultrasonic welding, or by the application of an adhesive.As described above, the pressure release vent member 120 can be a singlelayer, or alternatively, a laminate of two or more layers of materials.In such case, the pressure release vent member 120 can be bonded to theretainer 118 to form a subassembly that is then inserted into thecontainer 104 following the gasket 124 and the contact spring 122. ThePTC device 126 and the positive contact terminal 116 are then placed inthe open end of the container 104 to seal the electrochemical batterycell 100. Alternatively, the pressure release vent 120 can be bonded toboth the contact spring 122 and the retainer 118 by one of the methodsdescribed above.

The example embodiment of electrochemical battery cell 300 (FIG. 3)includes a crimped retainer 318 that is formed by placing the pressurerelease vent member 320 onto the retainer 318, placing the contactspring 322 onto the pressure release vent member 320, and then bendingthe edge of the retainer 318 so that it contacts the contact spring 310to form a subassembly. The pressure release vent member 320 can beoptionally bonded to the retainer 318 or to the contact spring 322 orboth the retainer and the contact spring. A similar subassembly can beformed for use in electrochemical battery cell 400 (FIG. 4). Where thecontact springs 322 and 422 include projections 332 and 432,respectively, the peripheral flanges of the contact springs 322 and 422are shaped to form one of many possible geometries, such as an annulusor polygon, with one of many possible profiles, such as a V-groove orrounded edge, before the contact springs are used to form thesubassemblies.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. For example, although the specification has describedprimarily lithium and lithium ion cells, the invention can also apply toother cell types. Also, while the embodiments described above haveillustrated a pressure release vent member associated with a positivecontact terminal that is connected to a cathode on discharge, the samerelease mechanism could be employed at a negative cell terminal.Therefore, the present embodiments are to be considered as illustrativeand not restrictive, and the invention is not to be limited to thedetails given herein, but may be modified, and is limited only by thescope of the appended claims.

1. An electrochemical battery cell comprising a housing, an electrodeassembly comprising a positive electrode, a negative electrode and aseparator disposed between the electrodes, and an electrolyte, thehousing comprising: a container with an open end in which the electrodeassembly and electrolyte are disposed; and a collector assembly,disposed between the electrode assembly and the open end of housing, thecollector assembly having: a contact spring, defining a pressure releasechannel, having at least one tab in electrical contact with either thepositive or the negative electrode; a pressure release vent closing thevent channel, said pressure release vent rupturing in response to apredetermined internal cell pressure; a retainer, also defining thepressure release channel, crimped in a C-shape around the contact springand the pressure release vent, said retainer forming a conductive pathwith the contact spring; and an insulating gasket disposed around theretainer, said insulating gasket separating the collector assembly frommaking electrical contact with the container and sealing the cell toprevent electrolyte leakage.
 2. The cell of claim 1, wherein thepressure release vent comprises at least a first layer of a compositionselected from the group consisting of: metal, polymer, and mixturesthereof.
 3. The cell of claim 1, wherein the pressure release vent has athickness of 0.254 mm or less.
 4. The cell of claim 1, wherein thecontact spring further comprises a peripheral flange forming acontinuous annulus surrounding the pressure release channel.
 5. The cellof claim 1, wherein the pressure release vent comprises a first layerhaving a vapor transmission rate of electrolyte less than 11.81g·mm/(day·mm²).
 6. The cell of claim 2, wherein the pressure releasevent comprises a second layer comprising a composition selected from thegroup consisting of: polyethylene, polypropylene, polybutyleneterephthalate, polyethylene terephthalate, ethylene acrylic acid,ethylene methacrylic acid, polyethylene methacrylic acid, and mixturesthereof.
 7. The cell of claim 6, wherein the pressure release ventcomprises a third layer, the first layer being disposed between thesecond layer and the third layer, and the third layer comprising acomposition selected from the group consisting of: polyethylene,polypropylene, polybutylene terephthalate, polyethylene terephthalate,ethylene acrylic acid, ethylene methacrylic acid, polyethylenemethacrylic acid, and mixtures thereof.
 8. The cell of claim 7, whereinthe first layer comprises aluminum.
 9. The cell of claim 1, wherein thecollector assembly comprises a second gasket disposed between theretainer and at least one of the contact spring and the pressure releasevent.
 10. The cell of claim 1, wherein the contact spring comprises acontinuous flange, surrounding the pressure release channel, thecontinuous flange having a continuous projection thereon.
 11. The cellof claim 1, wherein the retainer and the pressure release vent arebonded together.
 12. The cell of claim 10, wherein the contact springand the pressure release vent are bonded together.
 13. The cell of claim1, wherein the pressure release vent ruptures at a pressure that rangesfrom 10.5 kg/cm² to 42.3 kg/cm² at a temperature that ranges from 20° C.to 25° C.
 14. The cell of claim 1, wherein the pressure release ventcomprises a layer of a composition comprising aluminum, and the pressurerelease vent member has a maximum thickness of 0.254 mm.
 15. The cell ofclaim 14, wherein the pressure release vent comprises a second layer anda third layer of a composition selected from the group consisting ofpolyethylene, polypropylene, polybutylene terephthalate, polyethyleneterephthalate, ethylene acrylic acid, ethylene methacrylic acid,polyethylene methacrylic acid, and mixtures thereof.
 16. The cell ofclaim 15, wherein the cell further comprises a positive temperaturecoefficient device disposed between the contact terminal and theretainer.
 17. The cell of claim 16, wherein the positive electrodecomprises FeS₂ and the negative electrode comprises lithium metal. 18.The cell of claim 17, wherein the retainer has a peripheral edge that issubstantially circular.
 19. The cell of claim 18, wherein the housing iscylindrical.
 20. An electrochemical battery cell comprising a housing,an electrode assembly comprising a positive electrode, a negativeelectrode and a separator disposed between the electrodes, and anelectrolyte, the housing comprising: a container with an open end inwhich the electrode assembly and electrolyte are disposed; and acollector assembly disposed between the electrode assembly and the openend of housing, the collector assembly comprising: a contact terminal; aretainer that defines a first opening; a contact spring attached to theelectrode assembly, wherein the contact spring has a peripheral flangethat defines a second opening, the first and second opening defining anpressure release channel; and a pressure release vent member having aperipheral portion disposed between the retainer and the contact springand closing the pressure release channel between the first opening andthe second opening, the pressure release vent member capable ofrupturing in response to internal cell pressure that is at least as highas a predetermined release pressure thereby allowing matter to escapethrough the first opening of the retainer; wherein the retainer and thecontact spring flange form a conductive path between the electrodeassembly and the contact terminal cooperate with the pressure releasevent member to form a seal between the pressure release vent member andthe retainer; and wherein the retainer has a crimp that applies acompressive force to the pressure release vent member and the contactspring.
 21. The cell of claim 20, wherein the burst pressure of thepressure release vent member ranges from 10.5 kg/cm² to 42.3 kg/cm² at atemperature that ranges from 20° C. to 25° C.
 22. The cell of claim 20,wherein the pressure release vent member comprises at least a firstlayer of a composition selected from the group consisting of: metal,polymer and mixtures thereof.
 23. The cell of claim 22, wherein a firstlayer of the pressure release vent member comprises aluminum.
 24. Thecell of claim 23, wherein the pressure release vent member comprises asecond layer comprising a composition selected from the group consistingof: polyethylene, polypropylene, polybutylene terephthalate,polyethylene terephthalate, ethylene acrylic acid, ethylene methacrylicacid, polyethylene methacrylic acid, and mixtures thereof.
 25. The cellof claim 24, wherein the pressure release vent member comprises a thirdlayer, the first layer being disposed between the second layer and athird layer, and the third layer comprising a composition selected fromthe group consisting of: polyethylene, polypropylene, polybutyleneterephthalate, polyethylene terephthalate, ethylene acrylic acid,ethylene methacrylic acid, polyethylene methacrylic acid, and mixturesthereof.
 26. The cell of claim 25, wherein the second layer comprisespolyethylene and the third layer comprises polyethylene.
 27. The cell ofclaim 20, wherein the peripheral flange of the contact spring comprisesa continuous flange surrounding the first opening, the continuous flangehaving a continuous projection thereon.
 28. The cell of claim 27,wherein the retainer has a crimp that applies a compressive force to theperipheral portion of the pressure release vent member and theperipheral flange of the contact spring.
 29. The cell of claim 28,wherein the collector assembly further comprises: a gasket; and apositive temperature coefficient device disposed between the contactterminal and the retainer.
 30. The cell of claim 29, wherein theretainer and the pressure release vent member are bonded together. 31.The cell of claim 30, wherein the positive electrode comprises FeS₂ andthe negative electrode comprises lithium metal.
 32. The cell of claim30, wherein the retainer has a peripheral edge that is substantiallycircular.
 33. The cell of claim 30, wherein the housing is cylindrical.34. The cell of claim 1, wherein the collector assembly furthercomprises a contact terminal.
 35. The cell of claim 1, wherein thecollector assembly further comprises a PTC device.
 36. The cell of claim35, wherein the PTC device is disposed between the contact terminal andthe retainer.
 37. The cell of claim 1, wherein the collector assemblyfurther comprises an internal gasket.
 38. The cell of claim 37, whereinthe internal gasket has a shape selected from the group consisting of:an L-shape, a C-shape and a substantially flat washer.
 39. The cell ofclaim 10, wherein the continuous projection is a downward projectingannular groove.
 40. The cell of claim 39, wherein the annular groove hasa V-shaped profile.
 41. The cell of claim 4, wherein the peripheralflange has a downward and inward rolled edge.